1. Field of the Invention
The present invention relates generally to the visual inspection of objects, and, more particularly, to an inspection apparatus for inspecting the visual appearance of an object, such as an integrated circuit (IC) package, based upon information derived from images taken of the inspected object.
2. Description of the Prior Art
For integrated circuit parts, such as IC packages, inspection of their electrical performance characteristics and their visual appearance characteristics is very important. Visual features that are inspected include, for example, marks, symbols, printed alphanumeric characters, and/or other indicia provided on the integrated circuit package case to display, for example, the name of the product, the lot number, the name of the manufacturer, and so on, with the inspection seeking to determine if these marks, symbols, characters, and/or indicia are formed in a preferred alignment, such as along a straight line, without being crooked or otherwise misaligned; to determine if there are voids, rubbing-offs, chips, scratches, and so on in these marks; and to determine if there are scratches, chips, cracks, and blowouts on the molded integrated circuit case, and so forth.
The visual appearance inspections are very minute and delicate, requiring highly developed judgement skills on the part of the inspector, and, accordingly, it has been very difficult to implement a mechanical device for performing the inspection traditionally performed by skilled workers. When inspections are carried out by skilled workers, the inspection tends to lack reliability due to the differences in the visual criteria applied by different workers. In addition, the inspection speed is relatively low for human inspectors and the inspection operation cannot be performed continuously over a long period of time. Moreover, even for the same worker, the visual inspection criteria will vary depending upon the length of the inspecting period and the mood or disposition of the inspector.
In addition to the visual method of inspection performed by a skilled worker, it is known to perform an inspection of an object, such as an integrated circuit package, using an apparatus which uses information derived from an image formed from the object to be inspected. However, problems and other drawbacks have been associated with prior art apparatus for carrying out an inspection mechanically, these problems including insufficient recognition accuracy in assessing the quality of the appearance from the image information, insufficient inspection rates, and/or a lack of reliability. More specifically, for a visual appearance inspection it is preferred from the standpoint of efficiency during the manufacturing process to perform the inspection while the items to be inspected are being transported by a transporting device, such as a conveyor. However, when an item is transported by a conveyor, the reliability of inspection result is not sufficiently high because the inspection apparatus is not able to cope completely with various undesired situations, such as the occurrence of unevenness in the transportation of the inspected objects or an unintended change in the orientation of the object from a predetermined position or alignment due to a shift in position caused by vibrations or the like. While the transport speed of the objects to be inspected can be reduced to avoid the above-mentioned drawbacks, the resulting decrease in the overall inspection capability of the apparatus is inconsistent with the desired goal of reliable time and cost efficient inspection. In addition, the prior art apparatus is unable to accommodate a plurality of different types of objects to be inspected, and, accordingly, is not economically efficient where different types of objects are to be inspected.